Title: 2000 Evaluation of Replacement Brake Pads for Police Patrol Vehicles
Series: Bulletin
Author: NLECTC
Published: February 2001
Subject: Police Patrol Vehicles
pages: 12
bytes: 18KB

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available from this Web site or order a print copy from NLECTC at 800-248-
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National Law Enforcement and Corrections Technology Center
Bulletin
A Program of the National Institute of Justice
February 2001

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200 Evaluation of Replacement Brake Pads for Police Patrol Vehicles

During the past several years, it has become apparent that many law
enforcement agencies, when confronted with the need to replace the brake
pads on patrol vehicles in their fleets, are more concerned with the cost of the
replacement brake pads than with maintaining the optimum level of performance
that was designed into the police patrol package vehicle. Similarly, many
agencies use private vendors to perform their vehicle maintenance and repair
work and do not know or even think about what replacement components are
being used. The ability to stop, particularly under the extreme operating
conditions typically encountered in police patrol situations, is of critical
importance in the law enforcement fleet. Prior to 1997, there was little, if any,
information available to law enforcement fleet administrators to guide them in
making informed purchasing decisions.

In May 1997, the National Law Enforcement and Corrections Technology
Center (NLECTC) of the National Institute of Justice conducted a
comprehensive evaluation of replacement brake pads for police patrol
vehicles.[1] The evaluation was the first of its type.

In June 2000, the second comparative evaluation of replacement brake pads
for police patrol vehicles was performed. It was necessary due to changes in
the pad materials and designs available in the automotive aftermarket, and due
to changes in the vehicles themselves. It has been found that a brake pad
material that works well on one brand and model vehicle does not necessarily
work equally as well on a different brand or model vehicle. Clearly, the need
for this information within the law enforcement community, however, has not
changed. This NLECTC bulletin is a synopsis of the results of that evaluation; a
detailed report is also available that contains statistical analyses of the test data.
To order a copy of the full report, write or call NLECTC, P.O. Box 1160,
Rockville, MD 20849-1160, 800-248-2742; or download it from JUSTNET,
www.nlectc.org.

Major manufacturers of replacement brake pads for police vehicles were
invited to participate in the evaluation. Twelve companies and two Original
Equipment (OE) manufacturing companies (Ford and Chevrolet) were
evaluated. Eleven sets of brake pads were tested on the Chevrolet Impala and
13 sets were tested on the Ford Police Interceptor. See table 1 for a list of
brand names and edge codes.[2] Brake pads that are supplied with new
police-package vehicles were also tested. Several companies, however, did not
submit their products for testing. No recommendations can be made about
those companies' products.

The Test

Each brand of brake pad was subjected to four tests to measure its
performance under various conditions and determine pad and rotor wear
characteristics. The brake pads were tested on a 2000 Ford Police Interceptor
and a 2000 Chevrolet Impala. These two cars were used as test vehicles
because they represent the vast majority of police cars in service use by law
enforcement agencies at this time. Both vehicles were equipped with Antilock
Braking Systems (ABS).

Once the participating companies were identified and their brake pads
acquired, the brake pads and rotors were delivered to Greening Testing
Laboratories, Inc. Greening Laboratories coded and marked each brake pad
and rotor set so that they stayed together throughout the test process, and then
completed the initial burnishing [3] using computer-controlled dynamometers to
assure identical break-in.

Following burnishing, a practical evaluation was conducted using two
police-package vehicles produced by major American manufacturers, one
rear-wheel drive and one front-wheel drive. A detailed report with comparison
charts and other analyses were prepared and will be published and distributed
to law enforcement and other interested agencies.

Because driving conditions in different parts of the country vary widely, no
specific "winners" or "losers" were identified. It is important that your
department place the appropriate weights on those portions of the test data
most representative of the conditions that you may encounter. A sample
distribution of category weights is shown in table 2.

The test results may be used in two ways. First, they may be used to compare
the performance of a specific brake pad against the Original Equipment pads to
determine which will best meet the needs of your department. In this case, you
should emphasize those portions of the evaluation that come closest to reflecting
your agency operation, and thus the needs of your department. Second, the
overall test results may be used to adjust the manufacturer's bid or local
vendor's price for these brake pad brands. In each test category, the absolute
difference between a given brake pad and the Original Equipment brake pad is
divided by the OE brake pad's score, resulting in a "deviation factor." This
factor is then multiplied by a category weight, such as those listed in table 2, to
produce a weighted category score. The total of these weighted scores for a
particular brake pad is then used to adjust the brake pad's bid or local retail
price for comparison with the bid or price of the Original Equipment pads.

Readers familiar with the first replacement brake pad evaluation report,
published in April 1998, will notice several significant changes in both the test
methodologies employed and the primary focus of several of the tests, as well
as the removal of the brake pad and rotor wear tests. These changes were a
direct result of a meeting held in March 1998 after the draft of the first report
was completed. At this meeting, representatives from the participating brake
pad manufacturers, brake specialists from the vehicle manufacturers, and other
companies that supported the testing program provided feedback on the first
round of tests. 

While all participants agreed that this first attempt to evaluate replacement
brake pads for police vehicles was a positive "first step," it was noted that
several modifications to the methodology would further enhance the value of the
information presented. It was generally agreed that while the deceleration rate
attainable and stopping distances achieved in a panic stop are important to law
enforcement, far more decelerations are made under normal driving and traffic
conditions. Consequently, the group's recommendation was for future brake
pad test programs to focus more on comparing pedal effort required to maintain
a targeted deceleration rate, with particular attention paid to pedal force as it
relates to brake pad temperature. (Note: When braking to a targeted
deceleration rate, where the speed of the vehicle at brake application is the
same, the stopping distance should also theoretically be the same, making any
measurement of stopping distances irrelevant.) The brake pad and rotor wear
tests were also recommended to be discontinued, as they resulted from
extremely severe operating conditions performed over a relatively short period
of time. As such, these tests may not be an accurate predictor of achievable
brake pad and rotor life when used in normal police patrol service. 

When reviewing the test data summaries contained in this bulletin, the reader
should consider the following points:

1.--Generally speaking, when lower pedal force is required to maintain a given
deceleration rate, the brake pad is working more efficiently. Low pedal force
can reduce driver fatigue, particularly in "stop and go" (heavy traffic) situations,
or any time that frequent brake applications are required. It is also beneficial for
drivers who may be less able to apply higher levels of pressure to the brake
pedal.

2.--Low pedal force indicates that the friction material used in a given brake
pad is more effective than those materials that require more pedal force. The
more effective friction material could, in certain cases, translate into somewhat
faster brake pad or rotor wear.

3.--While a certain temperature level is necessary for proper functioning,
excessive heat is generally the enemy of any type of mechanical device or
system. In terms of brake system performance, excessively high temperatures
can contribute to premature breakdown of rubber components, such as hoses
and seals, as well as certain electronic components, such as ABS sensors. In
addition, as brake fluid absorbs moisture from the atmosphere, high operating
temperatures can raise the temperature of the brake fluid/water mixture in the
cylinders and calipers to the point where the moisture turns to steam, or
vaporizes. This produces a condition known as "vapor lock," resulting in
reduced braking capability (evidenced by a "spongy" feeling when the brake
pedal is depressed), or, in severe cases, the total loss of braking ability.

Ambient-Temperature (Cold) Braking Performance Test 

Law enforcement officers regularly begin their patrol shifts and respond to
emergency situations in a patrol vehicle that has been parked for several hours
and before normal or optimal operating temperatures have been reached. The
general stopping characteristics and the pedal force required when the brake
components are essentially cold are of significant importance.

Objective: Determine the stopping performance characteristics of the test brake
pads when the entire brake system is at ambient rather than normal or optimal
operating temperature.

Methodology: Each of the test brake pad/rotor sets was evaluated to determine
its cold temperature braking characteristics. This was accomplished by
performing 10 decelerations (at a specific predetermined location on the test
track) from 45 mph to 15 mph at a deceleration rate of 10 ft/s2. After each
deceleration, the test vehicle was accelerated back to 45 mph and driven for
approximately 2 miles (back to the predetermined deceleration point) to allow
the brake components to cool before the next deceleration in the series.
Temperature increase during each deceleration and brake pedal force
necessary to maintain the target deceleration rate were recorded. Table 3
shows the results from this test. Table 3a graphically shows the pedal force
comparisons. 

Normal-Operating-Temperature Braking Performance Test

Most of a law enforcement officer's day is spent on normal patrol, driving at
normal speeds. Heat produced in the braking system, and the resulting changes
in the pedal force required to make normal stops can be of great importance,
particularly for officers whose size, weight, or strength make them less able to
produce the higher pedal efforts required by some brake pad materials.

Objective: Determine the stopping performance characteristics of the test brake
pads under normal or optimal operating temperature conditions.

Methodology: Each of the test brake pad/rotor sets was evaluated to determine
its normal operating temperature braking characteristics. This was
accomplished by performing 15 decelerations (at a specific location on the test
track) from 60 mph to 20 mph at a deceleration rate of 15 ft/s2. After each
deceleration, the test vehicle was accelerated back to 60 mph and driven for
approximately 1 mile (to another predetermined deceleration location) to allow
the brake components to cool before the next deceleration in the series.
Temperature increases during each deceleration and throughout the entire test
process, as well as brake pedal force necessary to maintain the target
deceleration rate, were recorded. Table 4 shows the results from this test.
Table 4a graphically shows the pedal force comparisons.

Hot Pursuit (Fade Resistance) Braking Performance Test

Law enforcement officers regularly respond to emergency or pursuit situations
that require emergency driving, including frequent hard brake applications from
high speeds. The ability of the brakes to provide high deceleration rates without
significant brake fade and without unacceptable increases in pedal effort during
these extreme conditions is of critical importance to the success of the law
enforcement mission and to the safety of the officers and general public.

Objective: Determine the stopping performance characteristics and the
resistance to fade of the test brake pads under severe
high-operating-temperature conditions.

Methodology: Each of the test brake pad/rotor sets was evaluated to determine
its performance characteristics in a simulated "hot pursuit" mode. This was
accomplished by performing two decelerations in rapid succession from 90
mph to 0 mph at 22 ft/s2 to heat up the brake pads and rotors. These two "heat
up" stops were followed immediately by three decelerations, from 70 mph to
30 mph at a deceleration rate of 22 ft/s2, performed in rapid succession
(approximately 1/4-mile intervals). After this five-deceleration series, the test
vehicle remained stationary in a 3-minute heat soak. Following the heat soak,
the entire series of five decelerations was repeated 4 additional times for a total
of 25 decelerations. Temperature increases during each individual deceleration,
each deceleration series, and throughout the entire test process, as well as
brake pedal force necessary to maintain the target deceleration rate, were
recorded. Table 5 shows the results from this test. Table 5a graphically shows
the pedal force comparison.

"Panic" Stop (Antilock Braking Mode) Performance Test

Police patrol vehicles are subject to rigorous use. This includes frequent
maximum (panic stop) brake applications from high speeds. The ability of the
brake system to resist fade and allow the antilock system to function so that the
officer can maintain vehicle control is of critical importance.

Objective: Evaluate the performance characteristics of each brake pad set
when subjected to a series of sudden "panic" stops from 70 mph. 

Methodology: Each of the test brake pad/rotor sets was evaluated to determine
performance characteristics in a series of "panic" stops. This was accomplished
immediately after the "hot pursuit" portion of the evaluation was completed. This
was accomplished by performing two decelerations in rapid succession from 90
mph to 0 mph at 22 ft/s2 to heat up the brake pads and rotors. These two "heat
up" stops were followed immediately by three decelerations at the maximum
deceleration rate attainable (activating ABS if possible) and were performed in
rapid succession (approximately 1/4-mile intervals). After this five deceleration
series, the test vehicle remained stationary in a 4-minute heat soak. Following
the heat soak, the entire series of 5 decelerations was repeated 3 additional
times for a total of 20 decelerations. Temperature increases during each
individual deceleration, each deceleration series, and throughout the entire test
process, as well as the average deceleration rate attainable on each stop, were
recorded. Brake pedal force necessary to maintain the target deceleration rate
was recorded. Table 6 shows the results from this test. Table 6a graphically
shows projected stopping distance.

Footnotes

[1.] The tests were conducted by Independent Testing and Consulting, Inc.

[2.] An edge code contains specific information about a brake lining, including a
manufacturer's identification, a numeric code that references the lining type, and
alpha characters that indicate the initial friction properties of the lining. These
alpha characters describe a range of normal and hot friction values measured
when a 1-inch-square piece of friction material is subjected to varying
conditions of temperature, pressure, and rubbing speed on a test machine.

[3.] Brake pads are made of a combination of materials that are held together
with resin, which collects on the surface during the manufacturing process.
Burnishing is a procedure in which the resin is worn or "polished" off; this gives
the brake pads better initial performance and reduces smoking caused by the
resin burning off.

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The National Law Enforcement and Corrections Technology Center is
supported by Cooperative Agreement #96-MU-MU-K011 awarded by the
U.S. Department of Justice, National Institute of Justice. Analyses of test results
do not represent product approval or endorsement by the National Institute of
Justice, U.S. Department of Justice; the National Institute of Standards and
Technology, U.S. Department of Commerce; Independent Testing and
Consulting, Inc.; or Aspen Systems Corporation.

The National Institute of Justice is a component of the Office of Justice
Programs, which also includes the Bureau of Justice Assistance, Bureau of
Justice Statistics, Office of Juvenile Justice and Delinquency Prevention, and
Office for Victims of Crime.